The objectives of the proposed research are to quantitatively examine: (a) the influence of blood flow in the terminal arterial and venous arcades on the local heat transfer in peripheral tissue, (b) the effect of this terminal circulation on the freezing and thawing of surface tissue in cryosurgical applications, and (c) the transient freezing of tissue in the vicinity of large superficial veins located beneath a cryosurgical probe. This interdisciplinary project involves closely coordinated theoretical and experimental investigations. A new quantitative theory is advanced to predict how the local thermal interaction between blood-carrying vessels and their surrounding tissue matrix changes as vessel size, number density, flow velocity and direction vary with distance from the tissue surface. New theoretical models are also proposed to show how the local freezing of tissue is altered both by blood perfusion and the presence of major superficial veins. Parallel experimental studies are to be performed on whole-animal preparations to critically test the validity of the theories and to provide vascular input data for the models. The whole-animal experiments on rabbits and dogs shall include spatially refined steady-state and transient thermocouple measurements of local tissue and blood temperature at both normal and cryogenic temperatures and the preparation of vascular casts and hollow cast replicas. The in vivo experiments shall include fine-wire-heated measurements of local perfusion and intravascular measurements of temperature and flow in large superficial veins. Temperature and flow measurements will also be performed on tissue replicas and large-scale laboratory models constructed to simulate the freezing of tissue in the vicinity of large superficial veins during cryosurgical procedure.